Coupler assembly for an optical backplane system

ABSTRACT

A coupler assembly for an optical backplane system having a backplane and two or more circuit packs connected to that backplane. Each circuit pack has an optical transceiver and the backplane has an optical pipe (e.g., an array of waveguides) adapted to guide optical signals between the transceivers of different circuit packs. A coupler assembly is provided for each transceiver to couple light between that transceiver and the optical pipe. Advantageously, the coupler assembly has a movable optical element that can accommodate possible misalignment between the backplane and the circuit pack. In one embodiment, the movable optical element is an array of MEMS mirrors, each mirror adapted to direct light between an optical transmitter or receiver and the corresponding waveguide of the optical pipe.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/743,922, filed Dec. 23, 2003, and entitled “Coupler Assembly for anOptical Backplane System,” the teachings of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical circuits and, morespecifically, to printed circuit board assemblies having optical circuitcomponents.

2. Description of the Related Art

A modem telecommunications or computer system typically has a number ofprinted circuit boards (PCBs) or cards, which plug into a backplane ormotherboard. The backplane generally provides power to the PCBs and apathway by which the PCBs communicate with each other. For mostbackplanes, an electrical bus, which is typically a series of wires, isa primary means by which the communication between the PCBs takes place.Electrical transmission characteristics of the bus are defined by itsmaterial properties, the physical layout of the components, the clockspeed of the signals, etc. As complexity of telecommunications andcomputer systems increases, signals within backplanes are driven atincreased clock speeds. However, at relatively high clock speeds (e.g.,over 1 GHz), the performance of electrical buses may becomeunsatisfactory due to dispersion, crosstalk, and emission of andsusceptibility to electromagnetic radiation.

To overcome this problem, backplane systems in which signals aretransmitted through backplanes via both electrical and optical buseshave been proposed. For example, one such backplane system is disclosedin U.S. Pat. No. 6,005,991, the teachings of which are incorporatedherein by reference. However, one problem with optical backplane systemsis that relatively accurate alignment is required to properly couplelight between the backplane and the PCBs plugged into that backplane.For example, an optical bus of the backplane has to be sufficiently wellaligned with the corresponding optical pathways and/or optical devicesof the PCBs to provide reliable operation when the system is subjectedto mechanical vibrations and/or temperature-induced deformations. Inaddition, backplane and PCB manufacturing tolerances that are typicallyless stringent than the required backplane/PCB alignment precision haveto be appropriately accommodated.

SUMMARY OF THE INVENTION

Problems in the prior art are addressed, in accordance with theprinciples of the present invention, by a coupler assembly adapted tooptically couple a circuit pack to a backplane in an optical backplanesystem, which can accommodate possible misalignment between the circuitpack and the backplane and is adapted to correct (1) initialmisalignment typically present when the circuit pack is first connectedto the backplane and (2) without further intervention from an operator,subsequent misalignment typically caused by mechanical vibrations and/ortemperature-induced deformations. To this end, the coupler assembly mayemploy a movable optical element that can automatically track changes inthe relative position of the backplane and the circuit pack to maintaingood optical coupling. In one embodiment, the movable optical element isan array of MEMS mirrors, each mirror adapted to direct light between anoptical transmitter or receiver of the circuit pack and a correspondingwaveguide of the optical pipe in the backplane. In another embodiment,the movable optical element is an array of flexible optical fibers, eachcoupled between an optical transmitter or receiver and a correspondingwaveguide of the optical pipe. One end of each fiber is fixedlyconnected to the optical pipe and has an angled surface adapted todirect light between the fiber and waveguide. The other end of the fiberis fixedly connected to the optical transmitter/receiver such that thefiber flexibility permits relative orientation of the circuit pack andthe backplane to be perturbed without deterioration in the opticalcoupling.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a backplane/circuit-pack assemblyaccording to one embodiment of the present invention;

FIGS. 2A-B show three-dimensional perspective views of a circuit packand a coupler assembly that can be used in the backplane/circuit-packassembly of FIG. 1 according to one embodiment of the present invention;

FIG. 3 shows a cross-sectional view of a backplane/circuit-pack assemblyaccording to another embodiment of the present invention; and

FIGS. 4A-C show three-dimensional perspective views a coupler assemblythat can be used in the backplane/circuit-pack assembly of FIG. 3according to one embodiment of the present invention.

DETAILED DESCRIPTION

Reference herein to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment can be included in at least one embodiment of theinvention. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment, nor are separate or alternative embodiments mutuallyexclusive of other embodiments.

FIG. 1 shows a cross-sectional view of a backplane/circuit-pack assembly100 according to one embodiment of the present invention. Assembly 100has a backplane 102 having an optical pipe 104 adapted to transmitoptical signals through the backplane. In one embodiment, backplane 102is a printed circuit board having an integrated array of opticalwaveguides that forms optical pipe 104 similar to the optical waveguidesdescribed in an article by E. Griese, “A High-Performance HybridElectrical-Optical Interconnection Technology for High-Speed ElectronicSystems,” published in IEEE Transactions on Advanced Packaging, 2001,Vol. 24, No. 3, p. 375, the teachings of which are incorporated hereinby reference.

Backplane 102 supports two circuit packs 112 a-b, each connected to thebackplane using a corresponding connector 114. Each circuit pack 112 hasa PCB 118 with circuit elements 116, wherein connector 114 providespower and electrical connections to the circuit elements and, dependingon the implementation, may fix the circuit pack in place on backplane102. To transmit and receive optical signals through optical pipe 104,each circuit pack 112 has a transceiver package 122 comprising anoptical transceiver 124 and a coupler assembly 126. Each transceiver 124has (i) one or more optical transmitters adapted to convert electricalsignals into the corresponding optical signals for transmission throughbackplane 102 and (ii) one or more optical receivers (e.g.,photo-detectors) adapted to transform optical signals received viabackplane 102 into the corresponding electrical signals. Each couplerassembly 126 is inserted into an opening in backplane 102 and serves tooptically couple corresponding transceiver 124 to optical pipe 104. Foreach optical transmitter of the corresponding transceiver 124, couplerassembly 126 has a lens 132 and a movable mirror 134. Similarly, foreach optical receiver of that transceiver, coupler assembly 126 also hasa lens 132 and a movable mirror 134. Each lens 132 is adapted to eithercollimate light emitted from transceiver 124 or focus light enteringthat transceiver. Similarly, each mirror 134 is adapted to either couplethe collimated light into a corresponding waveguide of optical pipe 104or direct light from a waveguide of the optical pipe through lens 132 tothe corresponding receiver of transceiver 124. In FIG. 1, transceiverpackages 122 a and 122 b are illustratively shown as emitting andreceiving light, respectively. One skilled in the art will appreciatethat, using its different mirrors 134, each transceiver package 122 maysimultaneously transmit and receive optical signals.

When each circuit pack 112 is first mounted on backplane 102, the tiltangle of each mirror 134 is adjusted to obtain efficient opticalcoupling of receivers and transmitters of corresponding transceiver 124to the corresponding waveguides of optical pipe 104. More specifically,using control signals from a mirror controller (not shown), each mirror134 sweeps through a range of tilt angles until optical interconnectionis established. Then, the tilt angle is fine-tuned to optimize thatconnection. After the initial alignment, each transceiver package 122may be configured to monitor the interconnection quality and todynamically adjust the tilt angles of mirrors 134 to correct forpossible misalignment caused by mechanical vibrations and/or temperaturevariations. Advantageously, due to the use of movable mirrors 134 intransceiver packages 122, circuit packs 112 are relatively easy tocouple to optical pipe 104 of backplane 102. In addition, good opticalcoupling can be dynamically maintained during operation of assembly 100.

FIGS. 2A-B illustrate a circuit pack 212 and a coupler assembly 226 thatcan be used for each circuit pack 112 and coupler assembly 126,respectively, in backplane/circuit-pack assembly 100 according to oneembodiment of the present invention. More specifically, FIG. 2A shows athree-dimensional perspective view of coupler assembly 226 in a processof being connected to circuit pack 212, and FIG. 2B shows athree-dimensional exploded perspective view of that coupler assembly.

Referring to FIG. 2A, circuit pack 212 has a PCB 218 with a connector214, using which the circuit pack can be attached to a backplane (notshown). Connector 214 is similar to each connector 114 (FIG. 1) andprovides power and electrical connections to the circuit elements ofcircuit pack 212. Using an edge card connector 244 and alignment pins246, coupler assembly 226 is attached to a transceiver 224 mounted onPCB 218. Connector pair 244 provides electrical power and controlsignals to coupler assembly 226, while pins 246 guide an optical fiberarray 248 of the coupler assembly to properly mate with transceiver 224.At the end of array 248 facing movable mirrors 232, coupler assembly 226has an array of lenses (not visible in FIG. 2A) inside housing 250analogous to lenses 132 of each coupler assembly 126 (FIG. 1).

Referring to FIG. 2B, coupler assembly 226 has a MEMS chip 252 orientedat about 45 degree angle with respect to a ceramic base 256. In oneembodiment, MEMS chip 252 has sixteen individually movable mirrors 232arranged as illustratively shown in FIG. 2B. One skilled in the art willappreciate that a different MEMS chip having a different number ofmovable mirrors may similarly be used. Light enters and exits couplerassembly 226 through an optical window 258 in housing 250. For example,when circuit pack 212 is attached to backplane 102 (FIG. 1), light fromoptical pipe 104 enters coupler assembly 226 through window 258,reflects off a mirror 232, and is coupled into a corresponding opticalfiber of array 248. Similarly, light emitted from an optical fiber ofarray 248 reflects off a mirror 232, exits coupler assembly 226 throughwindow 258, and is coupled into optical pipe 104. A driver chip 254provides driving voltages used in MEMS chip 252 to appropriately andindividually tilt mirrors 232. A representative MEMS chip suitable foruse in coupler assembly 226 is disclosed in U.S. patent application Ser.No. 10/261,089, filed on Sept. 9, 2002 and entitled “Monolithic MEMSDevices for Optical Switches,” the teachings of which are incorporatedherein by reference.

FIG. 3 shows a cross-sectional view of a backplane/circuit pack assembly300 according to another embodiment of the present invention. Assembly300 is analogous to assembly 100 (FIG. 1) and has a backplane 302 havingan optical pipe 304 adapted to transmit optical signals. In oneembodiment, optical pipe 304 is an array of buried waveguides located atdepth d from an outer surface of backplane 302. Backplane 302 supportstwo circuit packs 312 a-b, which are similar to circuit packs 112 a-b ofassembly 100. More specifically, each circuit pack 312 has a PCB 318,circuit elements 316 mounted on the PCB, and a connector 314, whichprovides power and electrical connections to the circuit elements. Totransmit and receive optical signals through optical pipe 304, eachcircuit pack 312 has an optical transceiver 324 similar to correspondingtransceiver 124 of FIG. 1.

To couple transceiver 324 to optical pipe 304, backplane/circuit-pack300 has a coupler assembly 322 comprising heads 326 and 328. Head 326 isdisplaced with respect to head 328 when a flexure 330 connecting saidheads is deformed. Coupler assembly 322 has an array of optical fibers332, each adapted to couple a waveguide of optical pipe 304 totransceiver 324. Fibers 332 are flexible and are bent when head 326moves with respect to head 328. Each fiber 332 extends from an edge ofassembly 322 by length d. The end of this extension has an angledsurface oriented at about 45 degrees with respect to the fiber axis. Areflective layer (e.g., metal) deposited onto the angled surface forms aturning mirror, which couples light in and out of fiber 332 whilechanging the light propagation direction by about 90 degrees. Wheninserted into a slot in backplane 302, the angled fiber end lines upwith a corresponding waveguide of optical pipe 304 as shown in FIG. 3.The other end of each fiber 332 can be mated, using alignment pins 346that are similar to alignment pins 246 (FIG. 2), with transceiver 324.

Circuit pack 312 can be attached to backplane 302, for example, asfollows. First, head 328 is fixedly attached to backplane 302 such thatmirrors 334 of fibers 332 are aligned with the corresponding waveguidesof optical pipe 304 to provide efficient light coupling between thefibers and waveguides. In one embodiment, head 328 is affixed tobackplane 302 using one or more solder joints 350 as shown in FIG. 3.Second, alignment pins 346 of floating head 326 are partially insertedinto the matching holes in the housing of transceiver 324. Then, flexure330 is flexed to align connector 314 with the matching connector part(connector receptacle) on backplane 302. Finally, circuit pack 312 ispushed toward backplane 302 to fully insert alignment pins 346 intotransceiver 324 and secure connector 314 in the connector receptacle toarrive at the assembly structure shown in FIG. 3. Inbackplane/circuit-pack assembly 300, flexure 330 will typically be in adeformed state to accommodate a typically present mismatch between thepositions of (1) transceiver 324 and connector 314 in circuit pack 312and (2) the matching elements of coupler assembly 322 and backplane 302.Advantageously, coupler assembly 322 allows circuit pack 312 to bemounted on backplane 302 in a relatively simple and straightforwardfashion while providing efficient optical coupling.

FIGS. 4A-C illustrate a coupler assembly 422 that can be used as couplerassembly 322 in assembly 300 according to one embodiment of the presentinvention. More specifically, FIGS. 4A-B show two three-dimensionalperspective views of coupler assembly 422, and FIG. 4C shows athree-dimensional perspective view of coupler assembly 422 mounted on abackplane 402. A flexure 430 that connects heads 426 and 428 in assembly422 is a serpentine spring that can accommodate lateral headdisplacements. Fibers 432 and alignment pins 446 in assembly 422 aresimilar to fibers 332 and alignment pins 346, respectively, in assembly322 (FIG. 3). Angled ends 434 of fibers 432 are visible in the viewshown in FIG. 4B. A circuit pack similar to circuit pack 312 (FIG. 3)can be attached to coupler assembly 422 and backplane 402 shown in FIG.4C by inserting alignment pins 446 of floating head 426 into thematching holes in the transceiver housing on that circuit pack, matingthe circuit pack and backplane electrical connectors (not shown), andpushing the circuit pack toward backplane 402 to secure both optical andelectrical connections.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Although the present invention was described inreference to optical pipes comprising optical waveguides, the inventionmay similarly be practiced with optical pipes implemented using freespace optics. Various modifications of the described embodiments, aswell as other embodiments of the invention, which are apparent topersons skilled in the art to which the invention pertains are deemed tolie within the principle and scope of the invention as expressed in thefollowing claims.

1. A coupler assembly adapted to provide optical coupling between anoptical transceiver of a circuit pack and an optical pipe of abackplane, the coupler assembly comprising a mirror adapted to move withrespect to a base of the coupler assembly and to direct light betweenthe optical transceiver and the optical pipe, whereby said opticalcoupling is enabled.
 2. The coupler assembly of claim 1, wherein, ifthere is a misalignment between the backplane and the circuit pack, thecoupler assembly is adapted to substantially compensate the effect ofsaid misalignment on said optical coupling using said movement of saidmirror.
 3. The coupler assembly of claim 1, wherein said mirror is partof a MEMS device attached to the base of the coupler assembly.
 4. Thecoupler assembly of claim 3, wherein the coupler assembly is adapted toreceive electrical power for the MEMS device from the circuit pack. 5.The coupler assembly of claim 1, wherein the coupler assembly is adaptedto move the mirror in response to changes in relative orientation of thebackplane and the circuit pack to maintain said optical coupling.
 6. Thecoupler assembly of claim 1, wherein: the optical transceiver is adaptedto process two or more optical signals; and the coupler assemblycomprises said mirror and at least one other mirror, each of saidmirrors being adapted to move with respect to the base and to direct arespective optical signal between the optical pipe and the opticaltransceiver, wherein the coupler assembly is adapted to provide opticalcoupling for each of the two or more optical signals.
 7. The couplerassembly of claim 6, wherein the coupler assembly is adapted to adjustorientation of each of said mirrors to automatically track changes inrelative orientation of the backplane and the circuit pack to maintainthe optical coupling for each of the two or more optical signals.
 8. Thecoupler assembly of claim 6, further comprising a first plurality ofwaveguides, each waveguide of said first plurality adapted to beoptically coupled to the optical transceiver, wherein: the optical pipecomprises a second plurality of waveguides; and each of said movablemirrors is adapted to direct the respective optical signal between awaveguide of the first plurality and a waveguide of the second pluralityto provide optical coupling for said respective optical signal.
 9. Thecoupler assembly of claim 1, further comprising an optical waveguideadapted to be optically coupled to the optical transceiver, wherein themirror is adapted to direct an optical signal between the opticalwaveguide and the optical pipe.
 10. The coupler assembly of claim 1,wherein: the optical pipe comprises a first optical waveguide; themirror is adapted to direct an optical signal between the opticaltransceiver and the first optical waveguide; and the coupler assemblycomprises a second optical waveguide adapted to be optically coupled tothe optical transceiver, wherein the mirror is adapted to direct theoptical signal between the first and second optical waveguides.
 11. Acircuit pack adapted to be coupled to a backplane, said backplane havingan optical pipe adapted to transmit optical signals through thebackplane, said circuit pack comprising: a coupler adapted to opticallycouple (i) an optical transceiver of the circuit pack and (ii) theoptical pipe, said coupler comprising a mirror adapted to move withrespect to a base of the coupler and to direct light between the opticaltransceiver and the optical pipe, whereby optical coupling between theoptical transceiver and the optical pipe is enabled.
 12. The circuitpack of claim 11, wherein, if there is a misalignment between thebackplane and the circuit pack, the coupler is adapted to substantiallycompensate the effect of said misalignment on said optical couplingusing said movement of said mirror.
 13. The circuit pack of claim 11,wherein said mirror is part of a MEMS device attached to the base of thecoupler.
 14. The circuit pack of claim 11, wherein the coupler isadapted to move the mirror in response to changes in relativeorientation of the backplane and the circuit pack to maintain saidoptical coupling.
 15. The circuit pack of claim 11, wherein: the opticaltransceiver is adapted to process two or more optical signals; and thecoupler comprises said mirror and at least one other mirror, each ofsaid mirrors being adapted to move with respect to the base and todirect a respective optical signal between the optical pipe and theoptical transceiver, wherein the coupler is adapted to provide opticalcoupling for each of the two or more optical signals.
 16. The circuitpack of claim 15, wherein the coupler is adapted to adjust orientationof each of said mirrors to automatically track changes in relativeorientation of the backplane and the circuit pack to maintain theoptical coupling for each of the two or more optical signals.
 17. Thecircuit pack of claim 15, wherein: the coupler comprises a firstplurality of waveguides, each waveguide of said first plurality adaptedto be optically coupled to the optical transceiver; the optical pipecomprises a second plurality of waveguides; and each of said movablemirrors is adapted to direct the respective optical signal between awaveguide of the first plurality and a waveguide of the second pluralityto provide optical coupling for said respective optical signal.
 18. Thecircuit pack of claim 11, wherein the coupler comprises an opticalwaveguide adapted to be optically coupled to the optical transceiver,wherein the mirror is adapted to direct an optical signal between theoptical waveguide and the optical pipe.
 19. The circuit pack of claim11, wherein: the optical pipe comprises a first optical waveguide; themirror is adapted to direct an optical signal between the opticaltransceiver and the first optical waveguide; and the coupler comprises asecond optical waveguide adapted to be optically coupled to the opticaltransceiver, wherein the mirror is adapted to direct the optical signalbetween the first and second optical waveguides.
 20. A method ofoptically coupling an optical transceiver of a circuit pack and anoptical pipe of a backplane, the method comprising: moving a mirror withrespect to at least one of the circuit pack and the backplane to directlight between the optical transceiver and the optical pipe and toautomatically track changes in relative orientation of the backplane andthe circuit pack, whereby said optical coupling is enabled.